Okay so during the bitcoin fork my btc was stored on coinomi. Then after a while I transferred my BTC somewhere.
Now how can I get my BTG?
Add a btg wallet in the same coinomi, use M/44H/0H/0H as derivation path to get btg from btc that already were in your coinomi pre-split, or,
restore a wallet with a word seed in Coinomi from scratch. Do not alter the derivation path when adding the btg part of your wallet.